This project proposes the development of a new technique for improving the performance of medical ultrasound systems using microbubble-based contrast agents. The ultimate goal is the creation of an "excitation enhanced" imaging system that will have a higher sensitivity than current ultrasound scanners. Vascular contrast agents are capable of enhancing the visibility of blood flow by several orders of magnitude. However their performance is still not sufficient to reliably image perfusion and diagnose conditions such as myocardial ischemia or infarction. The excitation enhanced ultrasound modality utilizes two acoustic fields: onefor contrast agent excitation and one for imaging. The excitation field temporarily increases the number of contrast agent bubbles with a size close to resonance at the frequency of the imaging field. If the imaging field is applied immediately after the excitation burst, acoustic scattering from the excited bubbles is markedly stronger than without the application of the excitation field. An in vitro system was constructed as part of the Phase I effort and experiments conducted using this system have demonstrated enhancements of up to 12dB. The next step is to modify an ultrasound scanner to include the modality and to validate the clinical potential of the technique with a series of in vivo experiments. PROPOSED COMMERCIAL APPLICATION: Ultrasonic Imaging is now the second most widely used imaging modality after x-ray. It's usage has increased in recent years due to the development of ultrasonic specific contrast agents. The proposed research will accelerate the usefulness of contrast aganets for many significant clinical applications.